Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
In some types of hydrogen fuel cells, hydrogen is formed from a hydrogen-containing fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell.
A fuel cell system can include a fuel cell battery, including one or more fuel cells (e.g., a fuel cell stack), and a fuel source, such as a fuel tank or a hydrogen generator. Hydrogen generators that supply hydrogen gas to a fuel cell can be an integral part of a fuel cell system, or they can be removably coupled to the fuel cell system. A removable hydrogen generator can be replaced with another one when the hydrogen containing materials have been consumed. Removable hydrogen generators can be disposable (intended for only a one-time use). Both removable and permanently installed hydrogen generators can be refillable (intended for use multiple times) to replace consumed fuel composition.
Hydrogen generators can produce hydrogen using a variety of hydrogen-containing materials and a variety of methods for initiating the release of hydrogen gas. Some hydrogen-containing materials (fuels) can be heated to release hydrogen gas, such as in a chemical decomposition reaction.
For cost-effective hydrogen generation it is desirable to be able to use durable components of the hydrogen generator many times, replacing spent fuel with fresh material. To accomplish this, a replaceable fuel unit containing the fuel and minimal packaging can be inserted into a hydrogen generator containing heaters and other components. Close contact between the heaters and the fuel unit is desired for efficient heating. In some situations it is desirable to slide fuel units into and out of the hydrogen generator. This can lead to damage to the fuel unit or heaters. One approach is to use materials for the heaters and the fuel unit package that are able to withstand the forces of fuel unit insertion and removal, but this can add to the cost of both the hydrogen generator and the fuel unit.
An object of the invention is to provide a hydrogen generator in which spent fuel units can be replaced with fresh ones without damaging either the hydrogen generator or the fuel unit. Another object of the invention is to provide a hydrogen generator and replaceable fuel units that do not have to be made with unnecessarily expensive materials. Yet another object of the invention is to provide a hydrogen generator that is able to tolerate variability in fuel unit dimensions, particularly as a result of fuel unit shrinkage or swelling during use, while still maintaining good contact between the heater and the fuel unit.